Class TopKInEachNodeHandler.AACO

Maintains an array of AggregatedCategory. For space consideration, this is implemented as
a pair of arrays, ordinals and values, rather than one array of pairs.
Enumerated in ordinals are siblings,
potential nodes of the FacetResult tree
(i.e., the descendants of the root node, no deeper than the specified depth).
No more than K ( = FacetRequest.numResults)
siblings are enumerated.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.